fix own regression in 2.65 [#33643] Rotation does not work at certain zoom level

caused by not projecting points behind the perspective view,
even though this worked in 2.64 the values were flipped (rotating direction was reversed and the center point was flipped).

added V3D_PROJ_TEST_CLIP_NEAR, when omitted ED_view3d_project_*** will project points from behind a perspective view plane.

1 files changed, 10 insertions, 4 deletions

diff --git a/source/blender/editors/space_view3d/view3d_project.c b/source/blender/editors/space_view3d/view3d_project.c
index 6227a55a890..153d7a61cf7 100644
--- a/source/blender/editors/space_view3d/view3d_project.c
+++ b/source/blender/editors/space_view3d/view3d_project.c
@@ -134,13 +134,19 @@ static eV3DProjStatus ed_view3d_project__internal(ARegion *ar,
 	vec4[3] = 1.0;
 	mul_m4_v4(perspmat, vec4);
 
-	if (vec4[3] > (float)BL_NEAR_CLIP) {
-		const float fx = ((float)ar->winx / 2.0f) * (1.0f + vec4[0] / vec4[3]);
-		if (((flag & V3D_PROJ_TEST_CLIP_WIN) == 0) || (fx > 0 && fx < ar->winx)) {
-			const float fy = ((float)ar->winy / 2.0f) * (1.0f + vec4[1] / vec4[3]);
+	if (((flag & V3D_PROJ_TEST_CLIP_NEAR) == 0)  || (vec4[3] > (float)BL_NEAR_CLIP)) {
+		const float scalar = (vec4[3] != 0.0f) ? (1.0f / vec4[3]): 0.0f;
+		const float fx = ((float)ar->winx / 2.0f) * (1.0f + (vec4[0] * scalar));
+		if (((flag & V3D_PROJ_TEST_CLIP_WIN) == 0) || (fx > 0.0f && fx < (float)ar->winx)) {
+			const float fy = ((float)ar->winy / 2.0f) * (1.0f + (vec4[1] * scalar));
 			if (((flag & V3D_PROJ_TEST_CLIP_WIN) == 0) || (fy > 0.0f && fy < (float)ar->winy)) {
 				r_co[0] = floorf(fx);
 				r_co[1] = floorf(fy);
+
+				/* check if the point is behind the view, we need to flip in this case */
+				if (UNLIKELY((flag & V3D_PROJ_TEST_CLIP_NEAR) == 0) && (vec4[3] < 0.0f)) {
+					negate_v2(r_co);
+				}
 			}
 			else {
 				return V3D_PROJ_RET_CLIP_WIN;